Apparatus and a method for employing said apparatus to determine the low field resistance of dc-biased gunn diodes

ABSTRACT

A Gunn diode is DC-biased to its operating point. A negative pulse having an amplitude equal to the bias voltage is applied across the Gunn diode. A first sinewave signal having a given frequency and a selected magnitude is applied across the Gunn diode. A voltage probe is coupled by a switch to one input of a dual-trace oscilloscope to display the waveform of the voltage across the Gunn diode on the oscilloscope. A second sinewave signal having the given frequency is applied to the other input of the dual-trace oscilloscope. The displayed waveform of the second signal is adjusted in magnitude until it is superimposed upon the first waveform on the oscilloscope. A RMS voltmeter is coupled across the second input of the oscilloscope to measure the value of the voltage of the second signal and, hence, the voltage across the Gunn diode, after the two sinewave signals are superimposed. The switch is moved to a second position so that the output of an AC current probe is coupled to the first input of the oscilloscope. The current probe converts the current through the Gunn diode to a voltage and has a known calibration or ampere to voltage conversion factor. The voltage waveform produced by the current probe is displayed on the oscilloscope and the magnitude of the second sinewave signal is adjusted until it is superimposed upon this displayed waveform. The RMS voltmeter measures the value of this second sinewave signal after these two sinewave signals are superimposed. This latter value is equal to the voltage at the output of the current probe. This latter reading of the voltmeter is multiplied by the calibration factor to provide the value of the current flowing through the Gunn diode. Then the first reading of the voltmeter is divided by the second reading of the voltmeter to determine the low field resistance of the Gunn diode.

United States Patent [191 Reynolds [451 Jan. 1,1974

APPARATUS AND A METHOD FOR EMPLOYING SAID APPARATUS TO DETERMINE THE LOWFIELD RESISTANCE OF DC-BIASED GUNN DIODES lnventor:

Allan L. Reynolds, White Plains, NY.

International Telephone and Telegraph Corporation, Nutley, NJ.

Filed: Feb. 5, 1973 Appl. No.: 329,767

Assignee:

US. Cl. 324/158 D, 324/62 R Int. Cl. G0lr 31/22, GOir 27/02 Field ofSearch 324/158 D, 158 T,

References Cited UNITED STATES PATENTS 8/1951 Carpentier 324/121 R8/1958 Marino 324/158 D 6/1972 Ghafghaichi 324/158 D PrimaryExaminer-Rudolph V. Rolinec Assistant Examiner-Ernest F. KarlsenAltorneyC. Cornell Remsen, Jr. et a1.

bum

wave signal having a given frequency and a selected magnitude is appliedacross the Gunn diode. A voltage probe is coupled by a switch to oneinput of a dualtrace oscilloscope to display the waveform of the voltageacross the Gunn diode on the oscilloscope. A second sinewave signalhaving the given frequency is applied to the other input of thedual-trace oscilloscope. The displayed waveform of the second signal isadjusted in magnitude until it is superimposed upon the first waveformon the oscilloscope. A RMS voltmeter is coupled across the second inputof the oscilloscope to measure the value of the voltage of the secondsignal and, hence, the voltage across the Gunn diode, after the twosinewave signals are superimposed. The switch is moved to a secondposition so that the output of an AC current probe is coupled to thefirst input of the oscilloscope. The current probe converts the currentthrough the Gunn diode to a voltage and has a known calibration orampere to voltage conversion factor. The voltage waveform produced bythe current probe is displayed on the oscilloscope and the magnitude ofthe second sinewave signal is adjusted until it is superimposed uponthis displayed waveform. The RMS voltmeter measures the value of thissecond sinewave signal after these two sinewave signals aresuperimposed. This latter value is equal to the voltage at the output ofthe current probe. This latter reading of the voltmeter is multiplied bythe calibration factor to provide the value of the current flowingthrough the Gunn diode. Then the first reading of the voltmeter isdivided by the second reading of the voltmeter to determine the lowfield resistance of the Gunn diode.

23 Claims, 3 Drawing Figures 8\ SINE me vs GENERATOR a is ass ar P PULSca 0. c. BIAS 4 7"6ENERA7'OR c5 cum/v 0/005 5 I 'nv ur DUAL TRACE 2?OSCILLOSCOPIE la n C) 8 S/NE WA V5, ,43 GENERATOR R/as. vow/warm l4BACKGROUND OF THE INVENTION This relates to apparatus and a method ofemploying the apparatus to determine the low field resistance of aDC-(direct current) biased Gunn diode.

Knowledge of the low field resistance of DC-biased Gunn diodes is ofprime importance since it enables one to estimate the reliability(useful lifetime) of Gunn diodes.

In order for Gunn diodes to be used effectively, it is important thattheir so-called average active-layer temperature be limited to a valueless than some arbitrarily assigned temperature. This limitingtemperature depends on the nature of the particular construction of theGunn diode, the materials comprising it, and on other considerations.

Formulas can be developed using the theoretical framework of solid-statephysics which defines a relationship between the average active-layertemperature and a parameter characteristic of a given Gunn diode calledthe low field resistance. The low field resistance derives itsusefulness from the fact that it is approximately directly proportionalto the average absolute temperature of the active layer of the Gunndiode.

FIG. 1 illustrates the I-V (ampere-voltage) characteristic 3 of atypical Gunn'diode biased at a DC input of V, volts and 1,, amps. Itshould-be noted'thatfor terminal voltages V greater than V the Gunndiode exhibits a negative conductance characteristic. V, is defined asthe threshold voltage" and its corresponding current I, is defined asthe threshold current."

A. conventional method of determining the low field resistance of apositively biased Gunn diode involves injecting a negative voltage pulseacross the diode whose amplitude is made equal to the value of the DCbias plus or minus some small voltage increment, for instance, tially avoltage pulse of amplitude (V, 0.25) volts is impressed across theDC-biased Gunn diode. The width of the voltage pulse is short enough toprevent appreciable cooling during the pulse. The resulting currentpulse, is then measured by a suitably coupled AC probe coupled to anoscilloscope with the value of the current pulse I being. read from thegraticule of the screen of the oscilloscope. The process is thenrepeated with a second voltage pulse of having a magnitude (V 0.25)volts and the current I, is observed and measured from the graticule ofthe screen of the oscilloscope. The low field resistance, R,,, is thencapable of being determined by the equation R 0.5/(1 I ohms, where thecurrent is in amperes.

This prior art method of determining the low field resistance is wellknown for its lack of accuracy and reproducibility which renders itvirtually useless. The primary sources of error occur in the necessityfor estimating small increments 1025 volts of large pulse magnitudes(typically to 16 volts) on an oscilloscope graticule. Thus, themeasurements are (l) performed under conditions of poor resolution, (2)are ,dependent on the accuracy of the oscilloscope calibration and (3)are subject to any errors due to variation of the pulse's magnitude asameasurement is being made. As

$0.25 volt. This is illustrated in FIG. 1. Inipointed out hereinabove,these accumulated errors generally result in grossly inaccurate valuesof low field resistance.

SUMMARY OF THE INVENTION An object of the present invention is toprovide apparatus and a method of employing the apparatus to determinethe low field resistance of DC-biased Gunn diodes which overcomes thedisadvantage of the abovementioned prior art apparatus and method.

Another object of the present invention is to provide an improvedapparatus and method of employing the apparatus that does not rely uponthe accuracy of the oscilloscope or the reading of values using thegraticule of the oscilloscope.

Still another object of the present invention is to provide apparatusand a method of employing apparatus which enables obtaining meaningfulmeasurements of low field resistance of Gunn diodes having the advantageof accuracy, a high degree of reproducibility and ease of measurementwhich makes it well suited as a high volume production technique.

A feature of the present invention is the provision of a method fordetermining the low field resistance of a Gunn diode comprising thesteps of direct current biasing the Gunn diode to a selected operatingpoint; applying across the Gunn diode negative pulses having a firstgiven amplitude and a given width; applying a first altemating currentsignal having a second given amplitude different than the first givenamplitude and a predetermined frequency; coupling one trace input of adual-trace oscilloscope across the Gunn diode to display a firstwaveform having a first value of peak-to-' peak voltage equal to thevalue of the peak-to-peak voltage across the Gunn diode; coupling asecond alternating current signal having the predetermined frequency tothe other trace input of the oscilloscope to display a second waveform;adjusting the magnitude of the second waveform to superimpose the secondwaveform on the first waveform in the display of the oscilloscope;measuring the value of the peak-to-peak voltage of the second waveformwhen it is superimposed on the first waveform, the last mentioned valueof peak-topeak voltage being equal to the first value; coupling the oneinput of the oscilloscope to a given electrode of the Gunn diode todisplay a third waveform having a second value of peak-to-peak voltagerelated by a predetermined calibration factor to the current through theGunn diodeg adjusting the magnitude of the second waveform tosuperimpose the second waveform on the third waveform in the display ofthe oscilloscope; measuring the value of the peak-to-peak voltage valueof the second waveform when it is superimposed on the third waveform,the last mentioned value of peak-topeak voltage being equal to thesecond value; multiplying the second value by the calibration factor toobtain a value of the current flowing through the Gunn diode; anddividing the first value by the multiplied second value to determine thelow field resistance of the Gunn diode.

Another feature of the present invention is the provision of apparatusfor determining the low field resistance of a Gunn diode comprising: afirst source of direct current bias coupled across the Gunn diode tobias the Gunn diode to a selected operating point; a second source ofnegative pulses having a first given amplitude and a given width, thesecond source being coupled across the Gunn diode; a third source ofadjustable alternating current signals having a second given amplitudedifferent than the first given amplitude and a predetermined frequency,the third source being coupled across the Gunn diode; a dual-traceoscilloscope having a first trace input and a second trace input; afourth source of adjustable alternating current signals having thepredetermined frequency, the fourth source being coupled to one of thefirst and second inputs of the oscilloscope; a voltmeter coupled acrossthe output of the fourth source; a voltage probe coupled to oneelectrode of the Gunn diode; an alternating current probe coupled to theone electrode of the Gunn diode; and a switch to couple the voltageprobe to the other of the first and second inputs of the oscilloscopefor a first given period of time and to couple the current probe to theother of the first and second inputs of the oscilloscope for a secondgiven period of time immediately following the first period of time.

BRIEF DESCRIPTION OF THE DRAWING Above-mentioned and other features andobjects of this invention will become more apparent by reference to thefollowing description taken in conjunction with the accompanyingdrawing, in which:

FIG. 1 is an I-V characteristic of a typical Gunn diode DC-biased to aselected operating point illustrating the technique employed in theprior art for determining the low field resistance of DC-biased Gunndiodes;

FIG. 2 is a schematic diagram, partially in block form, of apparatus fordetermining the low field resistance of a DC-biased Gunn diode inaccordance with the principles of the present invention; and

FIG. 3 is an l-V characteristic of a typical Gunn diode biased to aselected operating point illustrating the method of employing theapparatus of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 2 there isillustrated therein apparatus in accordance with the principles of thepresent invention that enables determining the low field resistance of aGunn diode. Resistors R and R, are isolating resistors. Capacitors C andC are coupling capacitors and capacitor C, is a bypass capacitor.

A DC bias voltage from DC bias source 4 is coupled across Gunn diode 5to bias the Gunn diode to its anticipated operating point illustrated inFIG. 3 at point 6 defined by V, and I,. A negative pulse having a givenwidth and a magnitude equal to V, is supplied by generator 7 and iscoupled across Gunn diode 5. The negative pulse provided by generator 7should be capable of supplying 200-600 nanosecond width pulses at verylow duty cycles to prevent diode 5 from cooling during application ofthe pulse from generator 7. Generator 8 provides an alternating currentsignal, such as a sinewave signal, having a magnitude identified as V,which is coupled through capacitor C and resistor R across diode 5. Alower limit is placed on the minimum frequency of the sinusoidalwaveform provided by generator 5 since it is desirable that severalcycles of this waveform be contained within the pulse interval asillustrated at 9 of FIG. 3.

The remainder of the components of the apparatus of FIG. 2 includes avoltage probe 10 connected to the positive electrode of diode 5. Probe10 is connected through switch 11 when it is in contact with contact 1to the first trace input of a dual-trace oscilloscope 12. A secondalternating current signal generator 13 is coupled to the second traceinput of oscilloscope 12 and a RMS (root means square) voltmeter 14 iscoupled across the output of generator 13. Generator 13 is also asinusoidal generator producing a sinewave output sig nal having afrequency that is identical to the frequency of the sinewave outputsignal of generator 8 and whose magnitude is identified as V When switch11 is moved into contact with contact 2 an AC current probe 15 iscoupled to the positive electrode of diode 5 and to the first traceinput of oscilloscope 12. Current probe 15 is a known type of currentprobe that has a calibration or ampere-to-voltage conversion factorwherein so many amperes of current flowing through diode 5 is convertedto a unit of voltage for application to contact 2. For instance, thecalibration factor may be 0.2 amperes per volt or in other words 0.2amperes detected by probe 15 is converted to one unit of voltage byprobe 15 for coupling to contact 2.

The procedure for determining the low field resistance of diode 5 is asfollows:

With diode 5 DC biased at its operating point, namely V, and 1,, anegative pulse having a magnitude V, is injected across diode 5 bygenerator 7. The sinewave signal at the output of generator 8 isadjusted to a peak-to-pealt voltage of V, as observed on the screen ofthe oscilloscope 12 with switch 11 in contact with contact 1. Themagnitude of the voltage of signal generator 13 as shown on the screenof oscilloscope 12 is adjusted until it coincides in magnitude andfrequency with the waveform already displayed on the oscilloscopescreen. In other words the sinewave of generator 13 is superimposed uponthe displayed waveform connected to contact 1 on the screen ofoscilloscope 12. Thus, when the waveforms of the two inputs tooscilloscope 12 are superimposed on the screen of oscilloscope l2voltage V, equals voltage V, and the voltage V, is accurately measuredby voltmeter 14.

Next switch 11 is placed in contact with contact 2 and the voltagewaveform present at the output of probe 15, which is equal to thecurrent through diode 5 when multiplied by the calibration factor ofprobe 15, is applied to the first input of oscilloscope l2 and displayedon the screen thereof. The magnitude of the waveform at the output ofgenerator 13 is adjusted until the waveform of generator 13 issuperimposed upon the displayed waveform coupled to the first input ofoscilloscope 12. The resultant value of voltage V, is read on voltmeterl4 and multiplied by the calibration or conversion factor of probe 15 toprovide the value of current'flowing through diode 5. I

The low field resistance R, is then determined by solving the followingequation: R, V II where V, is the first reading taken on voltmeter 14when switch 10 is in contact with contact 1 and I 4 is the value ofvoltage as read on voltmeter 13 when switch 10 is in contact withcontact 2 multiplied by the calibration factor of probe 15.

While I have described above the principles of my invention inconnection with specific apparatus it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

I claim:

l. A method for determining the low field resistance of a Gunn diodecomprising the steps of:

direct current biasing saidGunn diode to a selected operating point; I

applying across said Gunn diode negative pulses having a first givenamplitude and a given width;

applying a first alternating current signal having a second givenamplitude different than said first given amplitude and a predeterminedfrequency;

coupling one trace input of a dual-trace oscilloscope across said Gunndiode to display a first waveform having a first value of peak-to-peakvoltage equal to the value of the peak-to-peak voltage across said Gunndiode; I

coupling a second alternating current signal having said predeterminedfrequency to the other trace input of said oscilloscope to display asecond waveform;

adjusting the magnitude of said second waveform to superimpose saidsecond waveform on said first waveform in said display of saidoscilloscope; measuring the value of the peak-to-peak voltage of saidsecond waveform when it is superimposed on said first waveform, the lastmentioned value of peak-to-peak voltage being equal to said first value;coupling said one input of said oscilloscope to a given electrode ofsaid Gunn diode to display a third waveform having a second value ofpeak-to-peak voltage related by a predetermined calibration factor tothe current flowing through said Gunn diode;

adjusting the magnitude of said second waveform to superimpose saidsecond waveform on said third waveform in said display of saidoscilloscope; measuring the value of the peak-to-peak voltage value ofsaid second waveform when it is superimposed on said third waveform,said last mentioned value of peak-'to-peak voltage being equal to saidsecond value; multiplying said second value by said calibration factorto obtain a value of the current flowing through said Gunn diode; anddividing said first value by said multiplied second value to determinethe low field resistance of said Gunn diode. 2. A method according toclaim 1,.wherein said selected operating point is determined by a givendirect current voltage, and said first given amplitude is equal to saidgiven direct current voltage. 3. A method according to claim 2, whereinsaid predetermined frequency is selected to provide a plurality ofcycles of said first and second alternating current signals during saidgiven width of said negative pulses. 4. A method according to claim 3,wherein said first and second alternating current signals are eachsinewave signals. 5. A method according to claim 4, wherein saidnegative pulses are low duty cycle pulses. 6. A method according toclaim 1, wherein said predetermined frequency is selected to provide aplurality of cycles of said first and second alternating current signalsduring said given width of said negative pulses. 7. A method accordingto claim 6, wherein said first and second alternating current signalsare each sinewave signals.

8. A method according to claim 7, wherein said negative pulses are lowduty cycle pulses.

9. A method according to claim 1, wherein said first and secondalternating current signals are each sinewave signals.

10. A method according to claim 9, wherein said negative pulses are lowduty cycle pulses.

11. A method according to claim 1 wherein said negative pulses are lowduty cycle pulses.

.12. Apparatus for determining the low field resistance of a Gunn diodecomprising:

a first source of direct current bias coupled across said Gunn diode tobias said Gunn diode to a selected operating point;

a second source of negative pulses having a first given amplitude and agiven width, said second source being coupled across said Gunn diode;

a third source of adjustable alternating current signals having a secondgiven amplitude different than said first given amplitude and apredetermined frequency, said third source being coupled across saidGunn diode;

a dual-trace oscilloscope having a first trace input and av second traceinput;

a fourth source of adjustable alternating current signals having saidpredetermined frequency, said fourth source being coupled to one of saidfirst and second inputs of said oscilloscope;

a voltmeter coupled across the output of said fourth source;

a voltage probe coupled to one electrode of said Gunn diode;

an alternating current probe coupled to said one electrode of said Gunndiode; and

a switch to couple said voltage probe to the other of said first andsecond inputs of said oscilloscope for a first given period of time andto couple said current probe to said other of said first and secondinputs of said oscilloscope for a second given period of timeimmediately following said first period of time.

13. Apparatus according to claim 12, wherein said voltmeter is a rootmean square voltmeter.

14. Apparatus according to claim 13, wherein said selected operatingpoint is determined by a given direct current voltage delivered by saidfirst source; and

said first given amplitude is equal to said given direct currentvoltage.

15. Apparatus according to claim 14, wherein said predeterminedfrequency is selected to provide a plurality of cycles of said first andsecond alternating current signals during siad given width of saidnegative pulses.

16. Apparatus according to claim 15, wherein said first and secondalternating current signals are each sinewave signals.

17. Apparatus according to claim 16, wherein said negative pulses arelow duty cycle pulses.

18. Apparatus according to claim 13, wherein said predeterminedfrequency is selected to provide a plurality of cycles of said first andsecond alternating current signals during said given width of saidnegative pulses.

19. Apparatus according to claim 18, wherein said first and secondalternating current signals are each sinewave signals.

22. Apparatus according to claim 21, wherein said negative pulses arelow duty cycle pulses.

23. Apparatus according to claim 13, wherein said negative pulses arelow duty cycle pulses.

1. A method for determining the low field resistance of a Gunn diodecomprising the steps of: direct current biasing said Gunn diode to aselected operating point; applying across said Gunn diode negativepulses having a first given amplitude and a given width; applying afirst alternating current signal having a second given amplitudedifferent than said first given amplitude and a predetermined frequency;coupling one trace input of a dual-trace oscilloscope across said Gunndiode to display a first waveform having a first value of peak-to-peakvoltage equal to the value of the peakto-peak voltage across said Gunndiode; coupling a second alternating current signal having saidpredetermined frequency to the other trace input of said oscilloscope todisplay a second waveform; adjusting the magnitude of said secondwaveform to superimpose said second waveform on said first waveform insaid display of said oscilloscope; measuring the value of thepeak-to-peak voltage of said second waveform when it is superimposed onsaid first waveform, the last mentioned value of peak-to-peak voltagebeing equal to said first value; coupling said one input of saidoscilloscope to a given electrode of said Gunn diode to display a thirdwaveform having a second value of peak-to-peak voltage related by apredetermined calibration factor to the current flowing through saidGunn diode; adjusting the magnitude of said second waveform tosuperimpose said second waveform on said third waveform in said displayof said oscilloscope; measuring the value of the peak-to-peak voltagevalue of said second waveform when it is superimposed on said thirdwaveform, said last mentioned value of peak-to-peak voltage being equalto said second value; multiplying said second value by said calibrationfactor to obtain a value of the current flowing through said Gunn diode;and dividing said first value by said multiplied second value todetermine the low field resistance of said Gunn diode.
 2. A methodaccording to claim 1, wherein said selected operating point isdetermined by a given direct current voltage, and said first givenamplitude is equal to said given direct current voltage.
 3. A methodaccording to claim 2, wherein said predetermined frequency is selectedto provide a plurality of cycles of said first and second alternatingcurrent signals during said given width of said negative pulses.
 4. Amethod according to claim 3, wherein said first and second alternatingcurrent signals are each sinewave signals.
 5. A method according toclaim 4, wherein said negative pulses are low duty cycle pulses.
 6. Amethod according to claim 1, wherein said predetermined frequency isselected to provide a plurality of cycles of said first and secondalternating current signals during said given width of said negativepulses.
 7. A method according to claim 6, wherein said first and secondalternating current signals are each sinewave signals.
 8. A methodaccording to claim 7, wherein said negative pulses are low duty cyclepulses.
 9. A method according to claim 1, wherein said first and secondalternating current signals are each sinewave signals.
 10. A methodaccording to claim 9, wherein said negative pulses are low duty cyclepulses.
 11. A method according to claim 1, wherein said negative pulsesare low duty cycle pulses.
 12. Apparatus for determining the low fieldresistance of a Gunn diode comprising: a first source of direct currentbias coupled across said Gunn diode to bias said Gunn dIode to aselected operating point; a second source of negative pulses having afirst given amplitude and a given width, said second source beingcoupled across said Gunn diode; a third source of adjustable alternatingcurrent signals having a second given amplitude different than saidfirst given amplitude and a predetermined frequency, said third sourcebeing coupled across said Gunn diode; a dual-trace oscilloscope having afirst trace input and a second trace input; a fourth source ofadjustable alternating current signals having said predeterminedfrequency, said fourth source being coupled to one of said first andsecond inputs of said oscilloscope; a voltmeter coupled across theoutput of said fourth source; a voltage probe coupled to one electrodeof said Gunn diode; an alternating current probe coupled to said oneelectrode of said Gunn diode; and a switch to couple said voltage probeto the other of said first and second inputs of said oscilloscope for afirst given period of time and to couple said current probe to saidother of said first and second inputs of said oscilloscope for a secondgiven period of time immediately following said first period of time.13. Apparatus according to claim 12, wherein said voltmeter is a rootmean square voltmeter.
 14. Apparatus according to claim 13, wherein saidselected operating point is determined by a given direct current voltagedelivered by said first source; and said first given amplitude is equalto said given direct current voltage.
 15. Apparatus according to claim14, wherein said predetermined frequency is selected to provide aplurality of cycles of said first and second alternating current signalsduring said given width of said negative pulses.
 16. Apparatus accordingto claim 15, wherein said first and second alternating current signalsare each sinewave signals.
 17. Apparatus according to claim 16, whereinsaid negative pulses are low duty cycle pulses.
 18. Apparatus accordingto claim 13, wherein said predetermined frequency is selected to providea plurality of cycles of said first and second alternating currentsignals during said given width of said negative pulses.
 19. Apparatusaccording to claim 18, wherein said first and second alternating currentsignals are each sinewave signals.
 20. Apparatus according to claim 19,wherein said negative pulses are low duty cycle pulses.
 21. Apparatusaccording to claim 13, wherein said first and second alternating currentsignals are each sinewave signals.
 22. Apparatus according to claim 21,wherein said negative pulses are low duty cycle pulses.
 23. Apparatusaccording to claim 13, wherein said negative pulses are low duty cyclepulses.